Method for forming platinum coating catalyst layer in reaction furnace ofr generating water gas

ABSTRACT

A barrier film which has uniform thickness and excellent adhesiveness to the base material and superbly functions to protect a platinum film can be formed on the inner wall surface of a moisture-generating reactor at ease and at a low cost.  
     The moisture-generating reactor in which hydrogen and oxygen are reacted to generate moisture without high temperature combustion is made of an alloy containing aluminum. A principally aluminum oxide (Al 2 O 3 )-composed barrier film is formed by applying an aluminum selective oxidation treatment on the inner wall surface of the moisture-generating reactor, and thereafter a platinum film is stacked on and stuck to the barrier film so that a platinum coating catalyst layer is formed.

FIELD OF THE INVENTION

The present invention is primarily concerned with improvements in themethod of manufacturing a moisture-generating reactor used insemiconductor manufacturing facilities and chemical manufacturingfacilities. More particularly, the present invention is concerned withthe process of forming a barrier film which constitutes a platinumcatalyst layer formed on the inner wall surface of a reaction spaceinside the reactor.

BACKGROUND OF THE INVENTION

For example, for affixing a silicon oxide film by means of a wateroxidation method in semiconductor manufacturing, continuous supply ofultra-high purity water is required. Consequently, the inventors of thepresent invention have developed a moisture-generating reactor as shownin FIG. 3 and disclosed it (see TOKU-KAI No. 2000-169109 and others).

The moisture-generating reactor is made by welding together reactor bodyparts 22, 23 which are placed opposite to each other so that a reactorbody having a reaction space P inside is formed. The reactor body isprovided with a material gas inlet 24, a moisture gas outlet 25, aninlet side reflector 26, an outlet side reflector 27 and others, and hasa platinum coating catalyst layer 28 on the inner wall surface of thereactor body part 23 on the side opposite to the material gas inlet 24.

More specifically, the afore-mentioned platinum coating catalyst layer28 is formed on the whole area of the inner surface of the reactor bodypart 23 made of SUS316L on the side of the moisture gas outlet 25. Aftera TiN-made barrier film 28 a has been formed on the inner surface of thereaction body part 23, a platinum film 28 b is formed thereon.

The thickness of the afore-mentioned barrier film 28 a is mostpreferably 0.1 μm to 5 μm. In the figure, the TiN barrier film 28 a witha thickness of about 5 μm is formed with an ion plating method.

Furthermore, a thickness of the afore-mentioned platinum film 28 b ispreferably 0.1 μm to 3 μm, and in the figure, the platinum film 28 b ofabout 3 μm thick is formed by the vacuum vapor deposition method.

As methods to form the barrier film 28 a, in addition to theafore-mentioned ion plating method, it is possible to employ an ionsputtering method, a PVD method such a vacuum vapor deposition methodand the like, a chemical vapor deposition method (CVD method), a hotpress method, a flame spray method and the like. As methods to form theplatinum film 28 b, in addition to the afore-mentioned vacuum vapordeposition method, it is possible to employ an ion plating method, anion sputtering method, a chemical vapor deposition method, a hot pressmethod and the like. In addition, if the barrier film 28 a is made of anelectrically conductive material such as TiN and the like, a platingmethod may be employed too.

The afore-mentioned barrier film 28 a is formed to prevent the loweringof the reaction rate of the platinum film 28 b occurring with thepassage of time.

Namely, as the temperature of a stainless steel base material rises dueto the reaction heat at the time of generating moisture, Ni and Fediffuse from the metal base material to the inside of the platinum film28 b. Ni and Fe as diffused are oxidized on the platinum film 28 b in anoxidation atmosphere, thus making the platinum film 28 b lose itscatalytic activity.

To prevent Fe and Ni from diffusing from the metal base material intothe platinum film 28 b, the afore-mentioned barrier film 28 a is formedon the surface of the stainless steel (base material).

For the afore-mentioned barrier film 28 a, materials not containing theelements such as Ni and Fe, and not producing oxides in the platinumcoating film are most preferred. It has been found that in addition tothe afore-mentioned TiN, not only TiAlN, TiC, TiCN and Al₂O₃ but alsooxides and nitrides such as Cr₂O₃, SiO₂, SrN and the like may be usedfor the barrier film 28 a.

Referring to FIG. 3, hydrogen and oxygen supplied through the materialgas inlet 24 into the reactor body are diffused by a diffusing membercomprising an inlet side reflector 26 and an outlet side reflector 27,and brought into contact with the platinum coating catalyst layer 28.When hydrogen and oxygen are brought into contact with the platinumcoating catalyst layer 28, reactivity of hydrogen and oxygen is raiseddue to the catalytic action of the platinum such that hydrogen andoxygen are brought in a so-called radicalized state. The radicalizedhydrogen and oxygen instantly react at the temperature (about 300°C.˜400° C.) lower than the combustion temperature of a hydrogen mixturegas such that moisture is produced without the high temperaturecombustion.

Generated moisture (moisture gas) is guided outside through the moisturegas outlet 25 and supplied to a semiconductor manufacturing chamber andthe like (not illustrated).

DESCRIPTION OF THE PRIOR ART

A moisture-generating reactor having a construction as illustrated inthe afore-mentioned FIG. 3 is permitted to make O₂ and H₂ react safelywith a reaction rate of almost 100% and without high temperaturecombustion, and continuously produce a required amount of moisture gasof ultra-high purity, thus achieving excellent, practical effects.

However, there remain some problems to solve in the above mentionedmoisture-generating reactor. One of the problems is concerned with theformation of the barrier film 28 a which constitutes a part of theafore-mentioned platinum coating catalyst layer 28.

That is, with the conventional moisture-generating reactor, the barrierfilm 28 a with thickness of 1-5 μm is formed by means of an ion platingmethod, an ion sputtering method, a vacuum deposition method and thelike. But, it is difficult to form the barrier film 28 a of uniformthickness such that the barrier film 28 a tends to have patches of adifferent thickness. In addition, there may be another problem such aspin holes formed on the barrier film 28 a.

It will become more difficult to form a barrier film 28 a with a uniformthickness on the inner wall surface of the reactor body part 23especially when an outlet side reflector 27 provided on the inner wallsurface of the reactor body part 23 is complicated in form.

Furthermore, it is quite costly to form the barrier film 28 a, therebymaking it difficult to reduce the manufacturing cost of thewater-generating reactor.

In addition, since adherence between the barrier film 28 a and thereactor body part 23 tends to be somewhat poor, there occurs so-calledfloating (i.e. separation) of the barrier film 28 a when a heat cycle isapplied.

OBJECT OF THE INVENTION

The present invention is aimed to solve the afore-mentioned problems ofthe conventional moisture generating reactor—that is (1) it is difficultto form the barrier film with a uniform thickness and with no pin holeson the inner wall surface in the reaction space; (2) it is difficult toreduce the cost for forming the barrier film; and (3) adherence of thebarrier film to the base material is somewhat poor. The presentinvention provides a method to form a platinum coating catalyst layer inthe moisture-generating reactor wherein a stainless steel alloycontaining Al is heat-treated for a prescribed time and at theprescribed temperature in an inert gas with the prescribed ratio ofhydrogen and water (H₂/H₂O), thereby making it possible to manufacture,using a so-called selective oxidation characteristic of the stainlessalloy, the barrier film comprising an almost 100% Al₂O₃ layer and aprincipally Al₂O₃ composed layer (i.e. a layer composed of principallyAl2O3) on the outer surface of the stainless steel alloy containing Alat an extremely low cost.

DISCLOSURE OF THE INVENTION

The present invention as claimed in Claim 1 has a basic construction inwhich a moisture-generating reactor having a platinum coating catalystlayer on the inner wall surface in the reaction space is formed,hydrogen and oxygen supplied into the reaction space are brought intocontact with the platinum coating catalyst layer and radicalizedthereby, and the radicalized hydrogen and oxygen are reacted to generatemoisture without the high temperature combustion wherein themoisture-generating reactor is made of an alloy containing aluminum, aprincipally aluminum oxide (Al₂O₃)-composed barrier film is formed byapplying an aluminum selective oxidation treatment on the inner wallsurface of the moisture-generating reactor, and thereafter a platinumlayer is stacked on and affixed to the barrier film so that a platinumcoating catalyst layer is formed.

Claim 2 relates to a process of forming a platinum coating catalystlayer as claimed in Claim 1 wherein a stainless steel alloy containingaluminum is employed for an alloy containing aluminum.

Claim 3 relates to a process of forming a platinum catalyst layer asclaimed in Claim 1 wherein the aluminum selective oxidation treatment iseffected on the alloy containing aluminum by heating for a prescribedtime under the conditions where the hydrogen-to-water (H₂/H₂O) ratio ina treatment atmosphere is 10⁴/1˜10⁹/1 and the heating temperature is300° C.-1500° C.

Claim 4 relates to a process of forming a platinum coating catalystlayer as claimed in Claim 1 wherein the platinum coating catalyst layeris formed on the inner wall surface of only a reactor body part on themoisture gas outlet side of the moisture generating reactor.

Claim 5 relates to a process of forming a platinum coating catalystlayer as claimed in Claim 1 wherein the barrier film which forms part ofthe platinum coating catalyst layer comprises an almost 100% aluminumoxide (Al₂O₃) layer on the inner wall surface of the base material and aprincipally aluminum oxide (Al₂O₃)-composed layer on the outsidethereof.

Claim 6 relates to a process of forming a platinum coating catalystlayer as claimed in Claim 2 wherein an austenitic alloy containingaluminum having chemical components of Cr 17.7 wt %, Ni 25.5 wt %, Mo0.01 wt %, Mn not more than 0.01 wt %, Al 3˜4 wt %, C not more than 0.01wt %, S not more than 0.01 wt %, P not more than 0.01 wt % and Fe theremainder is employed for the alloy containing aluminum.

Claim 7 relates to a process of forming a platinum coating catalystlayer as claimed in Claim 3 wherein the heating treatment is effected atthe temperature of 800° C. for 3 hours in the treatment atmosphere of anargon gas containing 10 VOL % hydrogen and 10 ppm water.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram (the Ellingham diagram) showing the relation betweenthe temperature and atmosphere (H₂/H₂O) at the oxidation of majorelements in the stainless alloy containing aluminum.

FIG. 2 is an atom composition graph of the Al₂O₃ film formed by applyingthe Al selective oxidation treatment on the surface of the stainlesssteel alloy containing aluminum (FR31).

FIG. 3 is a sectional schematic illustration of the conventionalmoisture generating reactor (TOKU-KAI No. 2000-169109).

LIST OF REFERENCE CHARACTERS AND NUMERALS

P designates a reaction space, 22 a reactor body part, 23 a reactor bodypart, 24 a material gas inlet, 25 a moisture gas outlet, 26 an inletside reflector, 27 an outlet side reflector, 28 a platinum coatingcatalyst layer, 28 a a barrier film, 28 b a platinum film and 29 afilter.

MODE OF CARRYING OUT THE INVENTION

FIG. 1 is the Ellingham diagram showing the relation between H₂/H₂O andthe temperature in the oxidation of each of the elements (Ni, Fe, Cr andAl) contained in the stainless steel alloy containing Al to be employedin the present invention. A curve A shows the oxidation of Ni, B theoxidation of Fe, C the oxidation of Cr and D the oxidation of Al.

As apparent from FIG. 1, it is possible to selectively oxidize only Alout of the elements Ni, Fe, Cr and Al by setting the value of H₂/H₂O(Vol ratio) in the oxidizing atmosphere and the temperature in theproper ranges. For example, only aluminum can be selectively oxidized inthe temperature range of 300° C.˜1500° C. when the H₂/H₂O ratio (volratio) is 10⁴/1˜10⁹/1.

For example, when only Al out of Ni, Fe, Cr and Al is to be selectivelyoxidized by setting the H₂/H₂O ratio value and temperature in the properranges, the oxidation of Al is expressed as below:Al₂O₃+3H₂←2Al+3H₂O

Also, Ni, Fe, and Cr oxides (NiO, Fe₂O₃, Cr₂O₃) are reduced as below:NiO+H₂→Ni+H₂OFe₂O₃+3H₂→2Fe+3H₂OCr₂O₃+3H₂→2Cr+3H₂O

The present invention relates to the forming of the barrier film Lcomprising a 100% Al₂O₃ layer and a principally Al₂O₃ composed layer onthe inner surface of the reactor body parts 22, 23 where the Alselective oxidation characteristic is utilized to oxidize Al alone onthe inner surface of the reactor body parts 22, 23 made of a stainlessalloy containing Al.

Embodiment

A stainless steel alloy containing Al (HR31) having a chemicalcomposition (wt %) listed at the upper section in Table 1 given belowwas used to produce the reactor body parts 22, 23 with an outsidediameter of 110 mm in a shape as shown in FIGS. 2 and 3. The lowersection in Table 1 is for the conventional stainless steel (SUS316L).TABLE 1 Chemical Composition (wt %) Fe Cr Ni Mo Mn Al C S P Austeniticremainder 17.7 25.5 0.01 <0.01 3˜4 <0.01 <0.01 <0.01 HR31 Austeniticremainder 17.2 15.1 2.76 <0.01 <0.01 <0.01 <0.01 <0.01 SUS316L

The pre-treatment step such as cleaning was applied on the inner surfaceof the reactor body part 23 made of the afore-mentioned Stainless steelalloy containing Al. After the inner surface was cleaned, the reactorbody part 23 was placed in the heat treatment furnace and heat-treatedunder the undermentioned conditions.

Conditions of Al Selective Oxidation

Ar gas containing 10% of H₂ and 10 ppm of H₂O is flowed into the heattreatment furnace (the inner volume of about 1 litre) at the flow rateof 1 litre/min, and the heat treatment was applied in the heat treatmentfurnace for about 3 hours while maintaining the temperature of the heattreatment furnace at about 800° C.

FIG. 2 is a depth profile (the result of the depth direction analysis)using the ESCA. The figure shows the element composition inside theAl₂O₃ film formed on the inner surface of the reactor body part 23 bymeans of the afore-mentioned Al selective oxidation treatment. Referringto FIG. 2, the curve E shows the atom number ratio (%) of Oxygen O, Fthe atom number (%) of Al, G the atom number (%) of Fe, H the atomnumber (%) of Ni, and I the atom number (%) of Cr. As apparent from FIG.2, the so-called Al-rich layer is formed in the range L within about 180nm (0.18 μm) from the inner side surface (adjacent the base material) ofthe Al₂O₃ film, and entirely Al₂O₃ composed layer is formed in the rangeL′ within about 50 nm (0.05 μm) from the inner side surface.

According to embodiments of the present invention, the reactor bodyparts 22, 23 are made of A stainless steel alloy containing Al. Theafore-mentioned Al selective oxidation treatment is applied on the innerwall surfaces of the reactor body parts to form the barrier film L whichis composed of principally Al2O3. Then, a platinum film 28 b is stackedon and affixed to the afore-mentioned barrier film L on the inner wallsurface of the reactor body part 23 on the moisture gas outlet side suchthat the moisture generating reactor is formed by placing theafore-mentioned reactor body part 23 and the reactor body part 22 on thematerial gas inlet 24 side opposite to each other, and welding togethertheir opposing outer peripheral surfaces where they contact.

According to the moisture generating test conducted using themoisture-generating reactor formed in accordance with this embodiment,it has been confirmed that in regard to the change of reactivity withthe passage of time, adhesiveness (mechanical strength) of the platinumcoating catalyst layer 28 and the likes, the moisture-generating reactoraccording to the present embodiment is never inferior to theconventional moisture generating reactor having a TiN barrier film 28 aformed by the iron plating method.

According to the afore-mentioned embodiment, the reactor body parts 22,23 are made of stainless steel alloy containing Al (austenite HR 31).However, it will be understood that any kind of material can be used aslong as it is an alloy containing Al.

Furthermore, according to this embodiment, about 0.18 μm thick layer Lcomposed of principally Al₂O₃, which is provided with a 0.05 μm thick100% (entirely) Al2O3 layer L′, is formed on the outer surface of thestainless steel alloy containing Al (the base material S) to serve asthe barrier film L. However, the thickness of the said Al₂O₃ layer L′andthe principally Al₂O₃ composed layer L can be appropriately chosen bychanging the conditions of the oxidation treatment in the Al selectiveoxidation.

In addition, according to this embodiment, the barrier film L is formedon both the reactor body parts 22, 23. However, the barrier film L canbe formed on the inner wall surface of only the reactor body part 23 onthe side of the moisture gas outlet 25.

Effects of the Invention

According to embodiments of the present invention, reactor body parts ofthe moisture-generating reactor are made of an alloy containing Al, anda principally Al₂O₃-composed barrier film is formed on the inner wallsurface of the reactor body parts by applying an Al selective oxidationtreatment thereon. Further, a platinum film is stacked on and affixed tothe barrier film to form a platinum coating catalyst layer.

As a result, in comparison with the case where the barrier film isformed by the conventional ion plating method or ion sputtering methodand the like, the principally Al₂O₃-composed barrier film with uniformthickness can be formed at ease and at a low cost, thus making itpossible to substantially reduce the manufacturing cost of themoisture-generating reactor.

The principally Al₂O₃-composed barrier film formed by theafore-mentioned Al selective oxidation is provided with excellentmechanical strength such as strong adhesiveness to the base material,and, at the same time, it functions superbly to block the invasion ofatoms constituting the base material into the platinum film, thusensuring a remarkably long service life of the platinum coating catalystlayer.

Thus, embodiments of the present invention achieve excellent, practicaleffects.

1. A process of forming a platinum coating catalyst layer in amoisture-generating reactor where a moisture-generating reactor having aplatinum coating catalyst layer on the inner wall surface in thereaction space is formed and hydrogen and oxygen supplied into thereaction space are both brought into contact with the platinum coatingcatalyst layer and radicalized thereby so that the radicalized hydrogenand oxygen are reacted to generate moisture without high temperaturecombustion wherein the moisture-generating reactor is made of an alloycontaining aluminum, a principally aluminum oxide (Al2O3)-composedbarrier film is formed by applying an aluminum selective oxidationtreatment on the inner wall surface of the moisture generating reactor,and thereafter a platinum layer is stacked on and affixed to the barrierfilm such that a platinum coating catalyst layer is formed.
 2. A processof forming a platinum coating catalyst layer in a moisture-generatingreactor as claimed in claim 1 wherein a stainless steel alloy containingaluminum is employed for the alloy containing aluminum.
 3. A process offorming a platinum coating catalyst layer in a moisture-generatingreactor as claimed in claim 1 wherein the aluminum selective oxidationtreatment of the alloy containing aluminum is effected by heating for aprescribed time under the conditions where the ratio of thehydrogen-to-moisture (H2/H2O) in the treatment atmosphere is 10⁴/1˜10⁹/1and the heating temperature is 300° C.-1500° C.
 4. A process of forminga platinum coating catalyst layer in the moisture-generating reactor asclaimed in claim 1 wherein the platinum coating catalyst layer is formedon the inner wall surface of only the reactor body part on the moisturegas outlet side of the moisture-generating reactor.
 5. A process offorming a platinum coating catalyst layer in the moisture-generatingreactor as claimed in claim 1 wherein the barrier film which forms partof the platinum coating catalyst layer comprises an almost 100% aluminumoxide (Al2O3) layer on the base material of the inner wall surface ofthe reactor body part and a principally aluminum oxide (Al2O3)-composedlayer on the outside thereof.
 6. A process of forming a platinum coatingcatalyst layer in the moisture-generating reactor as claimed in claim 2wherein the alloy containing aluminum is an . austenitic alloycontaining aluminum having chemical composition of 17.7 wt % of Cr, 25.5wt % of Ni, 0.01 wt % of Mo, not more than 0.01 wt % of Mn, 3 to 4 wt %of Al, not more than 0.01 wt % of C, not more than 0.01 wt % of S, notmore than 0.01 wt % of P and the remaining % of Fe is employed for analuminum containing alloy.
 7. A process of forming a platinum coatingcatalyst layer in the moisture-generating reactor as claimed in claim 3wherein the heating treatment is effected at the temperature of 800° C.for 3 hours in the treatment atmosphere of an argon gas containing 10VOL % hydrogen and 10 ppm water.